The present invention relates to atomic frequency standard and microwave technique, and more particularly to a certain kind of miniaturized microwave cavity for atomic frequency standard.
At present, there exist two kinds of similar microwave cavity. The first kind is loop-gap cavity that has been described by W. Froncisz and James S. Hyde (J. Mag. Reson. Vol. 47, 515. (1982)). This kind of cavity is also called slotted tube cavity (T. Sphicopoulos and F. Gardiol, IEE Proc., Vol.134, Pt. H, No.5, 405 (October 1987)). The second is described by H. Schweda, G. Busca and P. Rochat ( U.S. Pat. No. 5,387,881), and is called magnetron cavity (G. Mileti, I. Ruedi and H. Schweda, Proc. 7th EFTF, 515(1992)).
The above two kinds of cavity are characterized by placing a coaxial slotted tube in a cylindrical cavity body. The slotted tube is formed with a tubular structure by putting several (normally four) equally spaced tile-like electrodes together. The gaps between the electrodes are called slots. The electrode has the function of inductor, and the slot acts as a capacitor. So the slotted tube is in fact an inductive-capacitive structure. The resonant frequency of the microwave cavity is mainly determined by this inductive-capacitive structure, namely is determined by the structural parameters of the slotted tube. This type of cavity has the following advantages: 1. The cavity can be very small for a determined resonant frequency, since the slotted tube can be very small. 2. The slotted tube enhances the energy of microwave field and enables to obtain proper field mode, for example, TE.sub.011 mode. 3. The line width of microwave absorption is narrow therefore the Q factor of cavity is high. The difference between the two kinds of cavity mainly lies in the structure of slotted tubes. Electrodes are separated for the first kind of cavity, so it is necessary to cement them on a certain form of substrate material to constitute the entire slotted tube. This operation is very inconvenient, and usually results in deviations of structural parameters of the slotted tube from designed values. For the second kind of cavity, the electrodes and the cylindrical cavity body are firmly connected by metal, the slotted tube is a rigid structure. As the result, the parameters of the slotted tube, which depend on mechanical processing precision, can be controlled very precisely. Consequently, it has excellent performances. However, this kind of cavity has the shortcomings of complex structure and therefore high manufacturing cost. Furthermore, both designs of the two kinds of cavity haven't taken into account enhancing the microwave-filling factor by increasing the number of slots, further decreasing the cavity volume by loading dielectric material into the cavity, and finely adjusting the cavity frequency mechanically.